Low noise electron discharge device



Nov. 20, 1962 Filed 001,. 12, 1959 FIG. l

R. G. ROCKWELL LOW NOISE ELECTRON DISCHARGE DEVICE FIG.

2 Sheets-Sheet l ROBERT G. ROCKWELL BYu/( WV ATTORNEY NOV 20, 1962 R. G.ROCKWELL 3,065,374-

LOW NOISE ELECTRON DISCHARGE DEVICE Filed Oct. l2, 1959 2 Sheets-Sheet',2

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l Current e Sum of Thermal Noise I Noise Current Squared q2 I I u entWave IFrom Ante I ited by Ia we'ekf Current Wave Z -IIA ai Excited by VqF IG. 4 II 22 35 B2 FIG. 5

VIIll 79 INVENTOR.

ROBERT G. RocKwE'Ll.

mx/(Hm ATTORNEY United States Patent 3,665,374 LW NGISE ELECRONDISCHARGE DEVICE Robert G. Rockwell, Los Altos Hills, Calif., assignorto Varian Associates, Palo Alto, Calif., a corporation of CaliforniaFiled Oct. 12, 1959, Ser. No. 845,875 18 Claims. (Cl. S15- 5.34)

The present invention relates to electron discharge devices and moreparticularly to klystron tubes having an extremely low noise figure.

The use of electron discharge devices for amplifying relatively weakmicrowave signals is limited by the inherent internal noise of thedevice. in the past, klystron tubes have been considered as havinginherent high noise figures of the order of 25410 db whereas noisefigures as low as 6-11 db have Ibeen achieved with low noise travelingwave tubes and noise figures on the order of 3 db with backward waveamplifiers. A theory has been advanced without verification that lownoise guns might be used with klystrons to reduce their noise figures ashas been done with traveling wave tubes in the past.

The major difficulty in providing a klystron amplifier with a low noiseelectron gun such as has been utilized in traveling wave tubes is thehigher beam current which is required for adequate klystron gain, and upuntil now it has been assumed that high beam current and low noiseperformance were incompatible. Some of the reasons for this were that l)a larger impedance transformation is required which increases the lenseffect `by demanding a higher perveance gun; (2) a larger potentialvariation exists across the beam due to the space charge; and (3) thehigher current density required necessitates a higher cathodetemperature and hence a higher noise ligure. Furthermore, in order todevelop a low noise klystron, new assembly techniques are requiredbecause of the need for an entirely non-magnetic tube, which is notnecessary for most other klystrcns. In constructing a low noise klystronamplifier, it has been realized that of primary importance are thealignment of the low noise gun electrodes with the drift tube, alignmentof the drift tube over its entire length, alignment of the beam with themagnetic eld, elimination of the collector secondary electrons from thebeam and the cleanliness of the tube. By constructing a klystron tube inaccordance with the present invention a noise figure of 6.7 db wasobtained.

A by-product of the higher current in the high perveance gun of a lownoise klystron is a very wide dynamic range.

The object of the present invention is to provide a novel low noiseklystrony tube useful as an amplifier of relatively weak microwavesignals.

One feature of the present invention is the provision of a novel cathode-mounting means including a cathode, a first mounting member, aplurality of stilts supporting the cathode on the first mounting member,a second mounting member, and a plurality of stilts supporting the firstmounting member on the second mounting member, the cathode and thesecond mounting member being disposed in the same direction from thefirst mounting member whereby the position of the cathode with respectto the second mounting member is maintained substantially fixed over awide temperature range.

Another feature of the present invention is the provision of a novelelectron gun mounting assembly including a hollow gun mounting block,means for mounting an electron gun on the gun mounting block and axiallyaligned therewith, and a hollow gun mounting sleeve adapted for mountingon an electron discharge device, a surface of the gun mounting block anda surface of the gun mounting sleeve being mating conical surfaceswhere- 'icc lby the gun mounting sleeve can lbe mounted on the electrondischarge device and aligned with the axis thereof and then the gunmounting block with an electron gun mountedV thereon can `be mounted onthe gun mounting sleeve via said mating conical surfaces thereby tomount the electron gun axially of the electron discharge device.

Another feature of the present invention is the provision of a cathodemounting assembly including a cathode supported on a mounting member, aplurality of electrodes for mounting in front of the cathode, aplurality of insulator spacers, one to be positioned on each s'ide ofthe electrodes and the mounting member for keeping the electrodes andthe mounting member in insulated, spaced-apart relation, a rst retainingmember positioned against that spacer on the back of the mountingmem-ber, a second retaining member positioned against that spacer on thefront of the forwardmost electrode, a plurality of mounting screwsadapted -for connecting the first and the second retaining members andwith the mounting member, the electrodes, and the spacers positionedunder compression therebetween, and a plurality of hollow expansionmembers, one to be positioned between the head of each of the mountingscrews and the adjacent retaining member whereby each of the expansionmembers expands when heated and compensates for the expansion in therespective mounting screw thereby keeping the mounting member, theelectrodes, and the spacers under compression.

Another feature of the present invention is the provision of a noveldrift tube assembly in an electron discharge device -comprising twoaxially aligned drift tubes with an annular header supporting each ofthe drift tubes within the body of the electron discharge device andaxially aligned with the electron beam whereby the two drift tubesprovide a single uniform `drift space accurately aligned with the axisof the electron beam.

Another feature of the present invention is the provision of the noveldrift turbe assembly of the aforementioned feature including two hollowcylinders axially mounted adjacent one another, each closed at itsoutward end by one of said annular headers thereby providing an enlargedopening between the adjacent ends of said drift tubes whereby thereduced plasma radian frequency is increased and thus the requiredlength of the drift space is reduced.

Still another feature of the present invention is the provision of anovel magnetic field distorting member adapted to surround the meansIfor collecting the electron beam in an electron ldischarge device, saidfield distorting member provided with a taper on the end thereof whichsurrounds the inner end of the means for collecting the electron beamwhereby the magnetic field within' the means for collecting the electronbeam is distorted, thereby preventing secondary electrons from returningto the cavity resonator means within the electron discharge device fromthe means for collecting the electron beam.

Other obiects and advantages of the present invention will becomeapparent `from the specification taken in connection with theaccompanying drawings wherein,

FIG. 1 is a longitudinal cross sectional view of the low noise klystronembodiment of the present invention with the magnetic field distortingmeans .retracted from its operating position,

FIG. 2 is an enlarged view of the low noise gun assembly shown in FG. l,

FiG. 3 is a perspective View of the cathode mounting structure shown inFiG. 2,

FIG. 4 is an enlarged cross section view of the cathode shown in FIGS. 13.

FIG. 5 is an enlarged view of the collector assembly shown in FIG. l anddelineated by line 5--5 with the magnetic field distorting means inoperating position surrounding the collector, and

FIG. 6 is a graph showing a schematic of the low noise klystronembodiment of the present invention with a curve plotted for thecharacteristic impedance and curves plotted `for the noise currentsquared over the different regions of the low noise klystron amplifier.

Referring now to Ithe drawing, the present invention includes acylindrical main body portion 11 as of, for example, copper having amulti-diameter longitudinal bore 12 extending therethrough. Two hollowdrift tube supporting cylinders 13 and 14, as of copper, are positionedadjacent one another and axially aligned within a reduced diameterportion of the longitudinal bore 12. Axially aligned hollow cylindricaldrift tubes 15 and 16 are positioned in the outer ends of cylinders 13and 14 by annular headers 17 and 18, respectively. The drift tubes 15and 16 project outwardly from the cylinders 13 and 14 thereby providinga long, accurately aligned drift region from the outer end of drift tube15 to the outer end of drift tube 16. This construction provides a longuniform drift region which is extremely dilcult to provide by means ofmachining a single tu-be. Also by opening lup the drift region withincylinders 13 and 14 the reduced palsma radian frequency is increased andthus the length of the required drift region is reduced. The cylinders`13 and 14 could project in the opposite direction from that shown orcould be limited 'in length to the Width of the headers 17 and 18 aslong as the drift tubes 15 and 16 are rigidly supported. A drift tubeassembly such as that illustrated passed 99.7% of the electron -beamtherethrough.

Fixedly secured, as by brazing, within one end of the longitudinal bore12 of the main body 11 is a radially tapered annular header 19, as ofcopper, with a short input drift tube 21 projecting from the aperturetherethrough toward the drift tube 15. Axedly secured, as by brazing,within the other end of the longitudinal bore 12 of main body 11 is anarrow annular header 22, as of copper, with a short output drift tube23 projecting toward drift tube 16 from the aperture therethrough. Themain body 11 and the annular headers 19 and 17 define a re-entrant inputcavity resonator 24, and the main body 11 and the annular headers 1S and22 define a re-entrant output cavity resonator 25.

A bore 26 is provided through the main body 11 into cavity resonator 24for positioning a coaxial input assembly 27 therein.

Each of the cavity resonators 25 and 26 can be provided with a tunerassembly 31 including a flexible tuner diaphragm 32 sealed in a bore inthe main body 11 and actuated by a tuner rod 33 for changing theresonator frequency of the cavity resonator, but inasmuch as the tunerassembly does not constitute part of the present invention it will notbe described.

Afiixedly secured, as by ybrazing, to the main body 11 and sealing oftone end thereof adjacent the input cavity resonator 24 is a beamgenerating assembly 34. The beam generating assembly 34 includes acathode 35 made up of an emissive member 36 as of, for example,impregnated porous tungsten and a cup-shaped mounting member 37 as of,for example, molybdenum. The emissive portion 36 comprises a cylindricalpellet 36a with a proboscis 36b projecting forwardly therefrom having aflaredout cathode face 36e. The pellet 36a is held within a sleeve 37aprojecting from the bottom of the mounting member 37. The cathode issupported from a shoulder 37b projecting outwardly from the bottom ofthe mounting member 37. Three first mounting stilts 38 of, for example,molybdenum support the shoulder 37 on a first mounting ring member 39which is in turn supported by three second mounting stilts 41 of thesame material as the stilts 38 on a second mounting ring member 42, thecathode 35 and the second mounting ring member 42 being disposed in thesame direction from the first mounting member 41 so that the position ofthe cathode with respect to the second mounting ring member ismaintained substantially fixed over a wide temperature range. A focuselectrode 43, a first anode electrode 44, a second anode electrode 45,and a third anode electrode 46 are positioned in front of the cathode inthe direction opposite from the first mounting ring member 39, and aninsulator spacer ring 47 as of, for example, quartz is positioned oneach side of the electrodes and of the second mounting ring member. Theshapes for the electrodes were determined by use of an electrolytic tankas customary in the art for electron guns designed to be operated with anegative focus electrode potential of about 20% of the anode or rstelectrode potential.

A first retaining ring member 48 is positioned against that insulatorspacer ring on the back of the second mounting ring member, and a secondretaining ring member 49 is positioned against that spacer 47 on thefront of the forwardmost electrode. These retaining ring members 48 and49 are held together with the second mounting member 42, the electrodes43, 44, 45, and 46, and the spacers 47 positioned under compressiontherebetween by three mounting screws 51 of, for example, stainlesssteel which pass through apertured projections of the first retainingring member 49 and thread into tapped holes in the second retaining ringmember. A hollow cylindrical expansion member 52 as of, for example,copper is positioned between the heads of the screws 51 and theapertured projections of the first retaining ring member 48 so that thecompression on the second mounting ring member 42, the electrodes, andthe spacers 47 is not reduced when the mounting screws 51 expand afterheating up.

A hollow cylindrical inner heat shield 53 is supported by a flange onone end fixedly secured, as by brazing, to the first mounting ringmember 39, projects toward and surrounds the back end of the cathode 35,shield 53 being slotted to permit passage of the first mounting stilts38 therethrough. An outer heat shield 54 is supported by a flange on theend thereof ixedly secured, as by brazing, to the second mounting ringmember and projects rearwardly of the cathode 35 to surround the frontend of the cathode 35. A mounting cup 55 surrounds the rst mounting ringmember 38 and the heat shields 53 and 54 and is held in place by anoutwardly projecting flange on an end thereof, the outwardly projectingflange being positioned between the second mounting ring member '4Z andthe spacer 47 therebehind.

The second retaining ring member 49 is axially aligned with a hollowconical gun mounting block 56 by being positioned on an annular shoulderon the end thereof and is tixedly secured to the gun mounting block 56by means of screws 57 which thread into tapped holes in the block 56.The annular shoulder on the block 56 is notched to permit the mountingscrews 51 to extend through the second retaining ring member 49. The gunmounting block 56 is fixedly secured to and axially aligned with one endof a gun mounting sleeve 58 which has a conical interior surface whichmatches the conical exterior surface of the gun mounting block 56. Theother end of the gun mounting sleeve 59 is fixedly secured to the end ofthe main body 11 adjacent cavity resonator 24 by means of a brazebetween mating flanges on the sleeve 58 and the main body 11.

The vacuum seal around the beam generating assembly 34 includes a hollowcylinder 59 which is fixedly secured at one end, as by brazing, to anoutwardly projecting shoulder on the gun mounting sleeve 58 and is xedlysecured at the other end, as by brazing, to a hollow cylindrical gunsealing member 61 which surrounds the cathode, the electrodes and theirrespective mounting members. The other end of the gun sealing member 61is secured to a stem cup 62, the end of which is sealed closed by a stemsealing disk 63 as of, for example, ceramic. The stem sealing disk 63 isprovided with a aoeasr U plurality of apertures 64 therethrough whichare in tu-rn covered externally by stern hats 65. An apertured electrodepositioning plate 66 is positioned on the rearward end of the mountingcup 55 and lead wires 67 attached to each of the individual electrodes43, 44, 45 and 46 pass through standoff insulators 68 as of, forexample, ceramic and are then xedly secured to one of the individualstem hats 65'. Positioned within the cupped end of cathode 35 is aheater element 69, the lead wires 71 of which pass through an aperturein plate 66 and are connected to separate stem hats 65. A circular sprayplate 72 is positioned over the central aperture in plate 66 by means ofsupport rods 73 which pass through plate 66 and are atiixedly secured tothe outside surface of the mounting cup E5. Annular iange splash shields74 are positioned between the second mounting ring member 42 and thefocus electrode 43 and the iirst anode electrode 44 adjacent the spacers47 to prevent cathode material from being deposited upon the spacers 47which would thus cause arcing between the members insulated by spacers47. The klystron tube is evacuated through a tube 70 which is thenpinched off.

Fixedly secured to the annular header 22 at the end of the main body 1land sealing off that end thereofis a collector assembly 75 (see FG. 5)including a hollow cylindrical outer adapter '76 as of cupronickel, oneend of which is fixedly secured to the header 22 surrounding theaperture therethrough and the other end of which is secured to a sealingcup '77 as of platinum. The cup 77 is in turn secured, as by brazing, toone side of an insulator ring 7S as of, for example, ceramic, the otherend of the ring 77 being secured to an eyelet 79 as of platinum. Alsosecured to the eyelet 79 and positioned axially within the outer adapter76 is a hollow cylindrical inner adapter 8l as of cupronickel, the innerend of which is secured to an outwardly projecting iiange on the innerend of a hollow cylindrical collector S2 as of copper positioned axiallywithin and spaced from the inner adapter 81. The outward end ofcollector 32 is closed by a collector plug `33 as of copper, the innersurface of which is tapered in order to help prevent secondary electronemission. A hollow cylindrical field distorting member Sd as of, forexample, steel provided with a taper on one end thereof is adapted totit around the collector 82 Within the inner adapter 81 for distortingthe magnetic field within the collector 82 to thereby prevent secondaryelectrons from retraversing the drift region and inducing undesirednoise currents in the input cavity. This asymmetrical piece of steelappeared to be mandatory, for without it the noise figure of a low noiseklystron amplifier which had achieved a noise tigure of 6.7 db was aboutdb.

Since a section of an electron beam is like a section of a transmissionline, by analogy the electron beam can act as an impedance transformer.It has been shown that under usual conditions of operation a diode isessentially an exponential impedance transformer. Therefore, a low noiseelectron gun which includes a plurality of electrodes with differentvoltages applied thereto for minimum noise `figure acts as a section ofnon-uniform transmission line which exponentially transforms theexisting impedance of the beam at the virtual cathode to the requiredimpedance of the beam at the input cavity gap.

Referring now to lFIG. 6 the top of the graph shows a schematic diagramof a low noise klystron tube embodiment of the present invention showinga cathode, a three region low noise gun, and a drift space followed by aklystron circuit. Because of the various electrode voltages, it is shownin the middle of the graph that the characteristic beam impedance 'whichexists as a constant value through the drift space and the klystroncircuit is not constant in the region between the cathode and the lastelectrode on the low noise electron gun. The gun, then, transforms, theimpedance of the beam at the cathode to the impedance of the beam in thedrift space.

At the bottom of the graph in FIG. 5 is shown an approximate estimate ofcurves for the square of the different noise currents. The solid line isthe overall noise current wave. Up to the klystron circuit region theoverall noise current is the sum of the uncorrelated noise currentsexcited at the potential minimum by the full shot-noise fluctuations inthe current designated by the line of short dashes and the Rackuctuations in the electron velocity designated by the line of long andshort dashes. A minimum of overall noise current is believed to occur inthe vicinity of the second anode, and the drift space is made longenough to place the next minimum at the input cavity gap. In theklystron circuit region noise from the input coupli-ng antenna,indicated by the dotted line, and ampliiied noise current created at theklystron input cavity gap, indicated by the line of long dashes, add tothe overall noise current wave.

Several two-cavity, low noise klystron amplifiers of the present designhave been built `for operation in both the S-band and C-band frequencyranges, with a noise igure of 6.7 db being achieved for an S--bandampliiier and 9 db for a C-band amplifier.

The construction of the low-noise electron gun which performedsatisfactorily incorporated a type B impregnated cathode comprising a0.100 diameter tungsten pellet with a 0.030 proboscis on the end thereofflared out to a 0.040 cathode face. The spacing of the first anode fromthe end of the cathode was equal to the diameter of the cathode face,namely, 0.040; of the second anode from the -rst anode was 0.096, and ofthe third anode from the second anode was 0.122. This made the totallength of the low noise gun 0.258". None of these dimensions werenecessarily optimized as far as obtaining noise reduction is concerned;hence, it appears there is room in this area for improved noiseperformance. The design of the cathode with the flare on the end thereofwas aimed at reducing emission from the sides of the cathode proboscisand may well have helped reduce the noise figure by the manner in whichthe noise space charge waves were excited in the vicinity of thecathode.

Experimental data proved that for a low noise klystron amplifier of theconstruction` herein described optimum operation is achieved with afilament voltage of 9.5 volts, a focus electrode voltage of zero volts,a iirst anode voltage of 52 volts, a second anode voltage of 120 volts,a third anode voltage of 300 volts, a cavity voltage of 1400 volts and abeam current of 2 milliamperes. The optimum drift space between the lownoise electron gun and the klystron circuit was found to beapproximately 3" for an S-band amplifier and 11/2 was used for a C- bandamplifier, although the length of this latter drift space was notnecessarily optimized. A comparison of gain versus cavity voltage showedthat the maximum gain occurred at a cavity voltage of 1700volts, andthat at 1400 volts there would be only one db less gain, while goingfrom 1700 volts down to 1400 volts lowers the noise figure four db.Consequently, one would obviously choose 1400 rather than 1700 for thecavity voltage since there is more to be achieved in reduction of noisefigure than is to be lost in gain.

Dynamic range is defined as the range of variation of power output fromVthe levell of that power due to noise alone up to the saturation level.`Traveling wave tubes and backward wave ampliers have a dynamic range ofapproximately db. Recently it was reported that parametric amplifiershave exhibited a dynamic range of about db. Experimental data taken on alow noise'klystron amplier of the present construction showed a dynamicrange of 118 db above'the minimum output level due to noise' alone.

Since many changes could be made in the above construction and manyapparently widely different embodiments of the invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A cathode assembly for an electron discharge device comprising incombination a cathode, a rst mounting member, a plurality of stiltssupporting said cathode on said first mounting member, a second mountingmember, a plur-ality of stilts supporting said first mounting member onsaid second mounting member, said cathode and said second mountingmember being disposed in the same direction from said first mountingmember and the stilts supporting the first member on said second memberadapted to compensate for expansion and contraction of the stiltssupporting said cathode on said first mounting member whereby theposition of the cathode with respect to the second mounting member ismaintained substantially fixed for a Wide temperature range, andsupporting means for positioning said second mounting member in theelectron discharge device.

2. A cathode assembly of claim 1 including a hollow gun mounting block,means for mounting said second mounting member on said gun mountingblock axially aligned therewith, and a hollow gun mounting sleeveadapted for mounting on the electron discharge device, a surface of saidgun mounting block and a surface of said gun mounting sleeve -beingmating conical surfaces whereby said gun mounting sleeve is mounted onthe electron discharge device and aligned with the axis thereof and saidgun mounting block is mounted on said gun mounting sleeve via saidmating conical surfaces thereby to mount the cathode assembly axially ofthe electron discharge device.

3. The cathode assembly of claim l wherein said cathode includes anemissive member comprising a pellet with a proboscis projectingforwardly therefrom and outwardly flared on the forward end thereof anda mounting mem-ber provided with a sleeve projecting from an end thereofand adapted to hold said pellet, said mounting member being providedwith an outwardly projecting shoulder for mounting the cathode in theelectron discharge device.

4. A cathode assembly of claim 1 including a plurality of electrodesmounted in front of said cathode in the direction of said first mountingmember, a plurality of in sulator spacers one positioned on each side ofsaid electrodes and said second mounting member for keeping saidelectrodes and said second mounting member in insulated, spaced-apartrelation, a first retaining member positioned against the spacer on theback of said second mounting member, a second retaining memberpositioned against the spacer on the front of the forwardmost electrode,a plurality of mounting screws adapted for connecting said first -andsaid second retaining members and with said second mounting member, saidelectrodes and said spacers positioned under compression therebetween,and a plurality of hollow expansion members one positioned between thehead of each of said mounting screws and the adjacent retaining memberwhereby each of said expansion members expands when heated andcompensates for the expansion in the respective mounting screw therebykeeping said second mounting member, said electrodes and said spacersunder com-pression.

5. A cathode assembly of claim 4 including a hollow gun mounting blockhaving a flange on one end adapted for mounting said second retainingmember thereto and a hollow gun mounting sleeve adapted for mounting onthe electron discharge device, a surface of said gun mounting block anda surface of said gun mounting sleeve being mating conical surfaceswhereby the second retaining member is mounted on said gun mountingblock and aligned with the axis thereof, said gun mounting sleeve ismounted on the electron discharge device and aligned with the axisthereof, and said gun mounting block is mounted on said gun mountingsleeve via said mating conical surfaces thereby to mount the cathodeassembly axially of the electron discharge device.

6. In an electron discharge device including means for forming anelectron beam, means for collecting the electron beam land cavityresonator means disposed between the means for forming the electron beamand the means for collecting the electron beam, a drift t-ube assemblycomprising two axially aligned drift tubes and an annular headersupporting each of said drift tubes within the body of the electrondischarge device and axially aligned with the electron beam, wherebysaid two drift tubes provide a single uniform drift region accuratelyaligned with the axis of the electron beam.

7. The apparatus of claim 6 including two hollow cylinders axiallymounted adjacent one another, each closed at its outward end by one ofsaid annular headers providing an enlarged opening between the adjacentends of said drift tubes whereby the reduced plasma radian frequency isincreased and thus the required length of the drift space is reduced.

8. In an electron discharge device including means for forming anelectron beam, means for collecting the elcotron beam, and cavityresonator means disposed between the means for forming the electron beamand the means for collecting the electron beam, a magnetic fielddistorting member adapted to surround the means for collecting electronbeam and provided with a taper on the end thereof which surrounds theinner end of the means for collecting the electron beam whereby amagnetic field within the means for collecting the electron beam isdistorted thereby preventing secondary electrons from returning to thecavity resonator means from the means for collecting the electron beam.

9. A cathode for a low noise electron discharge device including anemissive member comprising a pellet with a proboscis projectingforwardly therefrom and outwardly flared on the forward end thereof anda mounting member provided with a sleeve projecting from an end thereofand adapted to hold said pellet, said mounting member provided withmeans for supporting the cathode in the electron discharge device.

l0. In a low noise electron discharge device including means forIforming an electron beam, means for collecting the electron beam andcavity resonator means disposed between the means for forming theelectron beam and the means for collecting the electron beam, a cathodeassembly including a cathode, a first mounting member, a plurality ofstilts supporting said cathode on said first mounting member, a secondmounting member, a plurality of stilts supporting said first mountingmember on said second mounting member, said cathode and said secondmounting member being disposed in the same direction from said firstmounting member whereby the position of the cathode with respect to thesecond mounting member is maintained substantially fixed over a widetemperature range; supporting means `for positioning said secondmounting member in the electron discharge device; and a drift tubeassembly axially aligned and disposed from said cathode assemblyincluding two axially aligned drift tubes and an annular headersupporting each of said drift tubes Within the body of the electrondischarge device and axially aligned' with the electron beam, wherebysaid two drift tubes provide a single uniform drift region accuratelyaligned with the axis of the electron beam.

ll. In a low noise electron discharge device including means for formingan electron beam, means for collecting the electron beam and cavityresonator means disposed between the means for forming the electron beamand the means for collecting the electron beam, a cathode assemblyincluding a cathode, a first mounting member, a plurality of stiltssupporting said cathode on said first mounting member, a second mountingmember, a plurality of stilts supporting said first mounting member onsaid second mounting member, said cathode and said second mountingmember being disposed in the same direction from said first mountingmember whereby the position of the cathode with respect to the secondmounting member is maintained substantially fixed over a widetemperature range; supporting means for positioning said second mountingmember in the electron discharge device; and a magnetic field distortingmember adapted to surround the means for collecting the electron `beamand provided with a taper on the end thereof which surrounds the innerend of the means for collecting the electron beam whereby a magneticfield applied to the means for collecting the electron beam is distortedthereby preventing secondary electrons from returning to the cavityresonator means from the means for collecting the electron beam.

12. The low noise electron discharge device ot claim 11 including adrift tube assembly in said cavity resonator means axially alignedwithin the electron discharge device and comprising two axially aligneddrift tubes, an annular header supporting each of said drift tubeswithin the body or the electron discharge device and axially alignedwith the electron tube, whereby said two drift tubes provide a driftregion accurately aligned with the axis of the electron beam.

13. The low noise electron discharge device of claim 11 including aplurality of electrodes for mounting in front of said cathode in thedirection opposite said first mounting member; a plurality of insulatorspacers one positioned on each side of said electrodes and' said secondmounting member for keeping said electrodes and said second mountingmember in insulated, spaced-apart relation; a rst retaining memberpositioned against the spacer on the back of said second mountingmember; a second retaining member positioned against the spacer on thefront of the forwardmost electrode; a plurality of mounting screwsadapted for connecting said rst and said second retaining members andwith said second mounting member, said electrodes and said spacerspositioned under compression therebetween; and a plurality of hollowexpansion members, one positioned between the head of each of saidmounting screws and the adjacent retaining member whereby each of saidexpansion members expands when heated and compensates for the expansionin the respective mounting screw thereby keeping said second mountingmember, said electrodes, and said spacers under compression.

14. The low noise electron discharge device of claim 13 including ahollow gun mounting block having a ange on one end thereof adapted formounting said second retaining member thereto and a hollow gun mountingsleeve adapted for mounting on the electron discharge device, a surfaceof said gun mounting block and a surface of said gun mounting sleevebeing mating conical surfaces, whereby the second retaining member ismounted on said gun mounting block and aligned with thc axis thereof,said gun mounting sleeve is mounted on the electron discharge device andaligned with the axis thereof, and said gun mounting block is mounted onsaid gun mounting sleeve via said mating conical surfaces thereby tomount the cathode assembly axially of the electron discharge device.

15. In an electron discharge device including means for forming anelectron beam, means for collecting the electron beam and cavityresonator means disposed between the means for forming the electron beamand the means for collecting the electron beam, a hollow gun mountingblock adapted for mounting of the means for forming the electron beamthereon and a hollow gun mounting sleeve adapted for mounting on thecavity resonator means, a surface of said gun mounting block and asurface of said gun mounting sleeve being mating conical surfaceswhereby the means for `forming the electron beam is mounted on said gunmounting block and aligned with the axis thereof, said gun mountingsleeve is mounted on the cavity resonator means and aligned with theaxis thereof, and said gun mounting block is mounted on said gunmounting sleeve via said mating conical surfaces thereby to mount themeans for forming the electron beam axialiy of said cavity resonatormeans.

16. in an electron discharge device including means for forming anelectron beam, means for collecting the electron beam, and cavityresonator means disposed between the means for forming the electron beamand the means for collecting the electron beam, means Afor positioning aplurality of electrodes in front of the mounting member which supportsthe cathode in. the means for forming the electron beam comprising aplurality of insulator spacers, one positioned on each side of theelectrodes and the mounting member for keeping the electrodes and themounting member in insulated, spacedapart relation; a first retainingmember positioned against the spacer on the back of the mounting member;a second retaining member positioned against the spacer on the front ofthe forwardmost electrode; a plurality of mounting screws adapted tforconnecting said first and said second retaining members with theelectrodes, the mounting member, and said spaces positioned undercompression therebetween; and a plurality of hollow expansion membersone positioned between the head of each of said mounting screws and theadjacent retaining member whereby each of said expansion members eX-pands when heated and compensates for the expansion in the respectivemounting screw thereby keeping the mounting member, the electrodes andsaid spacers under compression.

17. A cathode assembly for an electron discharge device comprising incombination a cathode, a rst mounting member, a support for said cathodeon said rst mounting member, a second mounting member, a support forsaid first mounting member on said second mounting member, said cathodeand said second mounting member being disposed in the same directionfrom said first mounting member and said support for .said firstmounting member 0n said second mounting member adapted to compensate forexpansion and contraction of said support for said cathode on said firstmounting member, whereby the position of the cathode with respect to thesecond mounting member is maintained substantially xed duringtemperature fluctuations, and supporting means ifor positioning saidsecond mounting member in the electron discharge device.

18. An electron discharge device including means for forming an electronbeam, means for collecting the electron beam, electron utilization meansdisposed between said means for forming the electron beam and said meansfor collecting the electron beam, mating conical mounting means on bothsaid means for forming the electron beam and said electron utilizationmeans for axially aligning said means for forming the electron beam withsaid electron utilization means.

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